Plated aluminum bearings



Oct. 9, 1956 E. L. COMBS ETAL 2,766,195

PLATED ALUMINUM BEARINGS Original Filed April 26, 1949 IN VEN TORS 4E2: ezze Z. (077(65 arles l'Fazest BY 62627772 $5cfiaer' Mala- M4 5 ATTORNEYS.

PLATED ALUMINUM BEGS Eugene L. (Iomhs, Euclid, and Charles L. Faust and Glenn R. Schaer, Columbus, Ohio, assignors, by mesne assignments, to American Brake Shoe Company, New York, N. ill, a corporation of Delaware Continuation of abandoned application Serial No. 89,592, April 26, 1949. This application January 26, 1953, derial No. 333,136

6 Claims. (Cl. 204-233) they are light in weight and, since aluminum is commercially available in large quantities, their cost would be low compared to certain other metallic bearings. Yet, only erratic success has been realized in the past with bearings made from aluminum or aluminum alloys. This lack of success is due to the formation during manufacture of the bearing, and also while in service, of a thin coating or film of aluminum oxide on the bearing surface. The aluminum oxide is hard relative to aluminum or aluminum alloys, and, thus, it is not conducive to good bearing performance, because it acts as an abrasive. The abrasive nature of the aluminum oxide causes aluminum bearings to wear unevenly, overheat, and break down readily, and, hence, their useful life is quite limited. The removal of the thin surface coating or film of aluminum oxide and the prevention of its recurrence would result in an aluminum or aluminum alloy bearing having excellent bearing characteristics, i. e., lightness and long life. Such a bearing might be obtained by removing the aluminum oxide from the surface of the bearing and then coating the surface with a material which has acceptable bearing characteristics and which prevents the reformation of aluminum oxide.

Electroplating on aluminum is recognized as being old in the art which most effectively began in 1928 with the description of methods by H. K. Work, Electroplating on Aluminum and its Alloys, Trans. Electro-chem. Soc., vol. L1H, p. 361 (1928). Since then, many investigations have been undertaken to apply adherent plated metal on aluminum. After many years of opportunity and development, two general procedures were 'i'ecognized as being available for plating on aluminum and its alloys, Trans. Electro-chem. Soc., 88, p. 307-324 (1945), H. Bengston. One procedure depends upon the application, first, of a zinc coating by chemical action. Subsequent plates are then applied to the zinc coating. The other procedure as disclosed in U. S. Patent 1,256,954 depends upon an electrochemically formed aluminum oxide coating on the surface of the aluminum. Subsequent plates are applied over the aluminum oxide coating.

Aduminum bearings plated by either of these two procedures would not meet the objects of the present invention. Prepared by the first, aluminum bearings would have an overlay of zinc which is not a metal that will give suitable bearing performance. Prepared by the second procedure, aluminum bearings would have an oxide coating on the surface. The presence of oxide in or 2,766,195 Patent-ed Get. 9, 1956 closely adjacent to, as would be the case of a 0.0005- inch tin overlay, the surface provides for the very opposite of the objectives of the present invention.

The prior art clearly implies that through no combination of treatment could one hope to achieve success toward the objectives of the present invention without using either a zinc coating or an oxide coating prior to electroplating. This is illustrated by discussion of the process represented in U. S. Patent 1,256,954, and The Monthly Review, February 1943, which discloses that when aluminum is so prepared and copper plated, there remains between the copper and the aluminum base metal the remnants of an anodic film.

It has been found that, contrary to the teachings of the prior art, neither oxide film, anodic treatment, nor a zinc film is required in producing firmly adherent copper and/0r tin overlays on aluminum bearings. The mechanism by which the procedure disclosed herein achieves the good plate adherence is not directly apparent from the operations or the results. It is believed that the good results are accomplished because any preformed oxide on the aluminum is removed and reformation is substantially eliminated in the sequence of operations in which the metal overlay or overlays are finally applied by electrodeposition.

it is an object of this invention to provide an aluminum-containing bearing characterized by the absence of aluminum oxide from its bearing surfaces.

it is another object of this invention to provide an I aluminum-containing bearing having a tightly adherent coating of tin on its aluminum oxide free bearing surfaces.

It is yet another object of this invention to provide an aluminum containing bearing having a tightly adherent and protective coating of copper, with an overlay of tin, on its aluminum oxide free bearing surfaces.

It is a further object of this invention to provide an aluminum containing bearing having an elec'trodeposited coating of tin intimately bonded to its bearing surface and having the interface bond between said tin and said aluminum bearing surface characterized by the absence of aluminum oxide.

It is a still further object of this invention to provide an aluminum containing bearing having an electrodeposited layer of copper intimately bonded to its hearing surface with an overlay of electrodeposited tin on said copper, and having the interface bond between said copper and said aluminum bearing surface free of aluminum oxide.

Other objects and advantages of the present invention will become apparent from the following detailed description thereof when read in conjunction with the accompanying drawing, in which Figure l is a microphotograph of a coated aluminum alloy specimen having an electrodeposited coating of copper on its surface with an overlay of tin and which has been metallographically polished without separation of the coatings.

Figure 2 is a microphotograp'h of another coated aluminum alloy specimen having an electrodeposited coating of copper on its surface with an overlay of tin and which has been metallographically polished with separation of the coatings.

It has been found that an aluminum containing hearing having a tightly adherent electrodeposited coating of a suitable bearing material such as tin on its bearing surface, or a tightly adherent electrodeposited coating of copper on its bearing surface with an overlay of electrodeposited tin, where the interface between the bearing surface and the electrodeposited layer is free of aluminum oxide, possesses excellent bearing characteristics. Such bearings Wear evenly, have long operational life, and do not overheat.

The tin coating can vary in thickness from 0.0001 to 0.010 inch depending on service requirements. Where copper is used with an overlay of tin, the copper coating can vary from 0.0001 to 0.002 inch thick, and the tin overlay can vary from 0.0005 to 0.001 inch.

It has been found that the process generally described below is admirably suited to the production of the bearings of this invention. In this process, the bearing, after manufacture, is cleaned of dirt, and oil, dipped in an acid solution to remove the thin film of aluminum oxide, and then electroplated with tin from a tin pyrophosphate bath. Alternatively, where it is desired to deposit copper instead of tin directly on the bearing, the copper can be electrodeposited on the cleaned and aluminum oxide free bearing surface from a copper pyrophosphate bath. Following this, tin is electrodeposited on the copper plate from a tin fluoborate bath.

The aluminum or aluminum alloy bearings to be coated with tin or copper are those that are commercially available in industry today. These alloy hearings can contain magnesium, silicon, or the other usual alloying constitucnts of aluminum well known to those skilled in the art. For the purposes of this invention bearings of aluminum or alloys thereof, where the base metal is aluminum, will be known as aluminum containing bearings.

The bearing surface of the machined and polished aluminum containing bearing should be cleaned of dirt and grease, and the aluminum oxide removed before the tin or copper is electroplated thereon to prevent a weak interface bond which will cause the recurrence of aluminum oxide after electroplating and separation of the tin or copper coating.

In the cleaning step any suitable method can be used which does not adversely affect the bearing and which removes the grease, dirt and other materials collecting on the surface of the bearing during its manufacture. It is preferred, however, to vapor or steam degrease the aluminum bearing to remove oil, grease, and dirt, or to use various hydrocarbon solvents for this purpose. After the degreasing step, the bearing can be scrubbed with an alkaline cleaner or immersed in an alkaline cleaning solution for a half minute or more until the bearing surface does not show Water breaks. After cleaning, the bearing should be rinsed in water to remove any of these cleaning materials.

When the bearing has been thoroughly cleaned as described above, it should be treated to remove the aluminum oxide film. This can be conveniently accomplished by dipping the bearing in an acid solution for a short period of time. It has been found desirable to use an oxalic acid-sulphuric acid solution as described in the patent of Charles L. Faust and John G. Beach, Patent No. 2,563,229, patented August 7, 1951.

The bearing is immersed in this solution for about five minutes at 100 F. to 170 F. The acid dipping solution should be a ten percent sulphuric acid solution (1.84 specific gravity) containing from one half to ten ounces per gallon of oxalic acid. After the material has been immersed in the acid dip for the required time, it is removed therefrom and rinsed.

Tin, which is an excellent bearing material, is now used to coat the cleaned and aluminum oxide free bearing. While many processes can be employed to coat the bearing with tin, it is preferred to electroplate the tin. This method provides a homogeneous coating of tin on the bearing surface, and the tin forms an intimate bond with the bearing surface of the aluminum containing bearing to prevent the recurrence of aluminum oxide. Furthermore, the electroplating process prevents the formation of aluminum oxide while the tin is being plated onto the bearing, and electroplating permits greater thicknesses of tin to be deposited than can be obtained by dipping or other methods. A tin pyrophosphate bath has been found best for electrodepositing the tin. A satisfactory bath composition which does not attack the aluminum during electroplating is as follows:

Stannous sulfate 46 Metallic tin 25 Potassium pyrophosphate 1'75 Ammonium hydroxide (0.90 sp. gr.) 0.75

This bath can be operated at a pH of 8, at a current densit of 25 amps/sq. ft. and at F. to provide excellent plates.

A hearing having a coating of copper with an overlay of tin is used, where, for reasons of economy, it is desirable to reduce the quantity of tin. The electrodeposited copper, like tin, forms a tightly adherent coating on the cleaned and aluminum oxide free surface of the aluminum containing bearing and prevents the recurrence of aluminum oxide during service operations. A satisfactory bath composition for electroplating copper onto the cleaned and aluminum oxide free aluminum containing bearing and which does not adversely affect the bearing is as follows:

G./l. Copper pyrophosphate 100 Potassium pyrophosphate 404 Ammonium hydroxide 3 Citric acid 10 Sufficient pyrophosphoric acid is added to this bath to produce a pH of about 8.2 to 8.8. The bath can now be operated at a current density of about 50 amps/sq. ft. and at a temperature of from F, to to produce an adherent coating of copper on the bearing.

Tin cannot be electrodeposited directly onto aluminum from a fluoborate bath, but it can be deposited on the electrodeposited copper coating. This process forms a convenient method of obtaining the tin overlay. A satisfactory bath for this purpose has the following composition:

Stannous fluoborate 200 Fluoboric acid 47 Boric acid 18 Hide glue 6 Licorice 1 Beta naphthol 1 Tin can be electroplated from this bath at a current density of 50 amps/sq. ft. and at a temperature of 75 F.

it is obvious to those skilled in the art that the above described baths and their operating conditions may be varied somewhat to obtain satisfactory plates.

In place of electrodeposited coatings of tin or of copper with an overlay of tin, it is to be understood that other metals having good bearing characteristics, i. e, lead, silver, cadmium, or indium can likewise be electrodeposited on aluminum bearings having a surface free of aluminum oxide. Binary alloys of these metals including copper and tin can also be employed when desired.

On testing the bearings of this invention by burnishing, no blisters were formed, indicating the absence of aluminum oxide at the interface. Furthermore, the mechanical forces acting away from the edge of the aluminum during rnetallographic polishing were insufiicient to pry the coatings away from the aluminum, showing the great strength-of the interface bond due to the absence of aluminum oxide. This result is shown in Figure 1 where a coated aluminum alloy of this invention has been metallographically polished without separation of the electrodeposited coatings. On the aluminum alloy 1 there was electrodeposited a coating 2 of copper with an overlay 3 of tin. Prior to polishing, a back-up plate 4 of nickel was applied to the tin overlay to assist in the metallographic preparation of the specimen. The tin layer appears black due to the uniform lapping-out of the soft tin between the harder nickel back-up plate and the c'opper'coating. This "lapping-out is a characteristic efiect encountered in metallographically polishing a specimen having adjacent hard and soft metals. In Figure 2 there is shown another coated aluminum alloy specimen which has been metallographically polished. It is believed that this aluminum alloy 5 contained aluminum oxide on its surface for on metallographical polishing, the electrodeposited copper layer 6 with its electrodeposited overlay 7 of tin separated from the aluminum alloy 5. The customary nickel back-up plate is indicated at 8. The black space 9 represents the base metal support for the specimen which showed up in the photograph through the area of separation of the copper coating from the aluminum alloy specimen.

In summary, the invention above described relates to an aluminum containing bearing having a tightly adherent electrodeposited coating of tin or other suitable bearing metal as set forth above, or of copper with an overlay of such bearing metal as tin, where the interface between said tin coating or said copper coating and the bearing surface is free of aluminum oxide. The copper or tin electrodeposited coating intimately bonded to the aluminum oxide free bearing surface prevents the formation of aluminum oxide during operation and thereby eliminates overheating and uneven wearing. It is thus obvious that these bearings have much greater usefulness than aluminum-containing bearings now available.

This application is a continuation of our application Serial No. 89,592, filed April 26, 1949, now abandoned.

We claim:

1. A method for producing tin-lined bearings having an aluminum-containing bearing shell comprising, subjecting the bearing shell to a cleaning step to remove dirt scums and the like, dipping the cleaned shell in a relatively Weak sulfuric-oxalic acid solution comprising a 10% sulfuric acid solution containing from about onehalf to ten ounces per gallon of oxalic acid for a period of time not substantially more than about five minutes and at an elevated temperature not substantially below 100 F. to remove all traces of aluminum oxide from the surface of the shell, thereafter electroplating the oxidefree surface of the shell With tin and to protect said oxidefree surface against further oxidation and to provide the bearing shell with a tin bearing lining.

2. A method for producing tin-lined bearings having an aluminum-containing bearing shell comprising, subjecting the bearing shell to a cleaning step to remove dirt scums and the like, dipping the cleaned shell in a relatively Weak sulfuric-oxalic acid solution comprising 10% sulfuric acid solution containing from about onehalf to ten ounces per gallon of oxalic acid for a period of time not substantially more than about five minutes and at an elevated temperature not substantially below 100 F. to remove all traces of aluminum oxide from the surface of the shell, thereafter electroplating the oxide-free surface of the shell With a tin lining of a thickness not substantially less than 0.0001 inch or substantially more than 0.01 inch to protect said oxide-free surface against further oxidation and to provide said bearing shell with a tin bearing lining.

3. A method for producing tin-lined bearings having an aluminum-containing bearing shell comprising, subjecting the bearing shell to a cleaning step to remove dirt scums and the like, dipping the cleaned shell in a relatively weak sulfuric-oxalic acid solution comprising a 10% sulfuric acid solution containing from about one-half to ten ounces per gallon of oxalic acid for a period of time not substantially more than about five minutes and at an elevated temperature not substantially below F. to remove all traces of aluminum oxide from the surface of the shell, thereafter electroplating the oxide-free surface of the shell with a copper lining of a thickness not substantially less than 0.0001 inch or substantially more than 0.002 inch to protect the oxide-frce surface against further oxidation, and thereafter applying a tin lining to said copper lining having a thickness not substantially less than 0.0005 inch or substantially more than 0.001 inch to provide said bearing shell with a tin bearing lining.

4. A method for producing tin-lined bearings having an aluminum-containing bearing shell comprising, dipping the shell in a sulfuric-oxalic acid solution comprising a 10% sulfuric acid solution containing from about onehalf to ten ounces per gallon of oxalic acid for such time and at such temperature to free the surface of the shell from all traces of aluminum oxide, thereafter providing the oxide-free surface of the bearing shell with a relatively thin and tightly adherent lining of tin to protect said oxide-free surface against further oxidation and to provide the bearing shell with a tin bearing lining.

5. A method for producing tin-lined bearings having an aluminum-containing bearing shell comprising, dipping the shell in a sulfuric-oxalic acid solution for a few minutes and at an elevated temperature to free the surface of the shell from all traces of aluminum oxide, said solution being approximately 10% sulfuric acid containing about one-half to ten ounces of oxalic acid per gallon of solution, thereafter providing the oxide-free surface of the bearing shell with a relatively thin and tightly adherent layer of copper to protect said oxide free surface against further oxidation, and thereafter forming a relatively thin lining of tightly adherent tin on said copper layer to provide the bearing shell with a tin bearing lining.

6. The method of removing aluminum-oxide from the surface of aluminum-containing bearing shells by means of a sulfuric-oxalic acid dip equivalent to a 10% sulfuric acid solution containing from about one-half to ten ounces per gallon of oxalic acid, and thereafter providing said oxide-free surface with a tightly adherent tin metal bearing lining.

References Cited in the file of this patent UNITED STATES PATENTS 1,457,149 Cunningham May 29, 1923 1,975,818 Work Oct. 9, 1934 2,086,841 Bagley et al. July 13, 1937 2,091,386 Viers Aug. 31, 1937 2,176,389 Brandt Oct. 17, 1939 2,563,229 Faust et al. Aug. 7, 1951 2,586,099 Schultz 1. Feb. 19, 1952 

3. A METHOD OF PRODUCING TIN-LINED BEARINGS HAVING AN ALUMINUM-CONTAINING BEARING SHELL COMPRISING, SUBJECTING THE BEARING SHELL TO A CLEANING STEP TO REMOVE DIRT SCRUMS AND THE LIKE, DIPPING THE CLEANED SHELL IN A RELATIVELY WEAK SULFURIC-OXALIC ACID SOLUTION COMPRISING A 10% SULFURIC ACID SOLUTION CONTAINING FROM ABOUT ONE-HALF TO TEN OUNCES PER GALLON OF OXALIC ACID FOR A PERIOD OF TIME NOT SUBSTANTIALLY MORE THAN ABOUT FIVE MINUTES AND AT AN ELEVATED TEMPERATURE NOT SUBSTANTIALLY BELOW 100* F. TO REMOVE ALL TRACES OF ALUMINUM OXIDE FROM THE SURFACE OF THE SHELL, THEREAFTER ELECTROPLATING THE OXIDE-FREE SURFACE OF THE SHELL WITH A COPPER LINING OF A THICKNESS NOT 